It was brand new 2 days ago, I haven’t done enough to mess up the extruder gear yet.
(I checked anyway & it looks fine)
As it is, you may be right about the filament diameter.
That being said, regardless of what is different, It’s now working near perfectly 
I may at some point go change the filament diameter setting in Cura & test the extrusion length,
but I’m now afraid of going away from what I know works well.